That could be a translation problem. Mine is in Dutch so YMMV.
Does your set-top box have a symbol that it is connected to your TV (a small remote symbol)?
Do you have a magic remote? What happens if you press the direct-tv button (looks like a small tv)?

Problem is, I use it on a Mac and can not really help you here.
Maybe you can find your answer here on the serviio.org website. Can not imagine that you can not acces a NAS with it.
Or here in a youtube tutorial

I had live tv for some time but my provider had problems so I changed to a provider who used a settopbox.
First I had the same problem as you but I managed to solve it. I don't know for sure that I did reset the tv but I had to choose the settopbox from the connector menu. A bit like this old tutorial:
old tutorial
The problem was that after this part they ask for your provider and the type of settopbox and that last was a bit difficult to find.
But, when I got it all working, I can use my magic remote to change channels and when I push the live-tv button it wil bring me back to the settopbox input
Good luck,
Peter

I noticed the standard build in apps from LG are a bit primitive. You can better look for apps that play music or use DLNA servers from you computer that can display the content much better. Examples are Serviio or Plex but there are more.

I see you have a wired connection to internet. Maybe that's your problem. Disconnect the network cable and try it again.
Normally a wired connection is better but if you have problems with it, disconnect it.
Good luck.

I have one thing you could try. It looks like the LG tv also supports NTFS. What you could try is use an NTFS formatted HD to see if it is possible to record more clips. Maybe the NTFS implementation is better than the FAT implementation in WEB OS.

A long time ago I also had this problem (but I don't think it was with the LG tv). What I had to do was set the screen mode on 'game' or 'movie'. This way the tv doen't process the image and the delay is minimal.
Hope this helps.